This invention relates to a hydraulic power operating system for the brakes of a vehicle, the system being adapted to obtain hydraulic fluid under pressure from, at first, the hydraulic power steering system of the vehicle other than that which is available directly from a source of hydraulic fluid and thereafter only from the source through a flow divider.
It has heretofore been known in the art that there exist two types of hydraulic power braking system. One of the types is that in which the hydraulic power system is so arranged in a hydraulic fluid circuit as to form in series the source of hydraulic fluid, the hydraulic power steering system and the power braking system so that the power braking system obtains hydraulic fluid from the precedingly located steering system. The other system has an unloading valve regulator or flow divider which controls the flow from the source so as to supply a portion thereof to the power steering system and remainder of the flow to the braking system regardless of whether any one or both of the two systems are actuated or not.
The first type is beneficially enabled to completely utilize whole quantity of fluid discharged from the source but is considered to be disadvantageous in that, a pressure drop is caused by actuating the preceding steering system and accordingly the power braking system is obliged disadvantageously to receive the resultant lower level pressure fluid from the steering system. In order to compensate for such pressure drop, the supply source is also obliged to be preset a larger supplying ability, i.e., capacity and accordingly a larger volume of space for equipment.
The second type is considered to be advantageous in utilizing the higher range of fluid pressure discharged from the supply source, but is considered disadvantageous in that, merely a portion of the flow from the source is utilized for actuating the power braking system so that a larger supplying ability is also required.
It may be fairly safely mentioned that, for prompt operation purpose, a comparatively larger quantity of fluid flow is desirable in actuating the power braking system at the early stage of the operation than is required at the subsequant stage of the operation. The reason is that a considerable quantity of fluid is required in order to compensate for a quantity of fluid consumed for an idling stroke (e.g. the displacement of the brake show across the gap between the rest position of the shoe and the drum) of a power piston in the wheel cylinder of the brakes and to compensate for any strain usually exhibited by all the associating parts of the braking system, such as for example, resiliently restorable expansion of conduits forming the system due to the fluid pressure.
In order to safely brake a traveling vehicle, it is desireable to decrease the above mentioned idling period of time by supplying a larger quantity of fluid at the first stage of braking operation.
On the other hand, in order to effect sufficient and prompt braking force in the second stage, the pressure drop by actuating the steering device is undesirable.
The first type of present day hydraulic braking systems is able to suit the former condition but is unable to meet the latter requirement and with the second type the reversal takes place.
A solution is now demanded to provide means to meet both of such inconsistent requirements for a hydraulic power operating system having a series of a hydraulic fluid supplying source, a power steering system and a power braking system.